1. Field of the Invention
This invention relates generally to an ultrasonic system and, more particularly, to an ultrasonic system which is compatible for use in either a sonic rangefinder photographic camera or in a general purpose sonic rangefinder designer's kit.
2. Description of the Prior Art
Ultrasonic ranging systems are conventionally used in cameras to effect automatic focusing, in instruments for monitoring liquid level in containers, for proximity detectors, etc. U.S. Pat. No. 4,199,246, entitled "Ultrasonic Ranging System for a Camera," by J. Muggli, issued Apr. 22, 1980, in common assignment herewith and now incorporated by reference herein in its entirety, is an example of an ultrasonic ranging system incorporated into a camera. The system in this patent transmits a burst of sonic energy towards a subject, and the transmit time measured from the burst to receipt of an echo is a measure of the subject range based on the assumption that the speed of sound is a constant.
In the patent referred to above, a single transducer is used to both transmit the sonic energy and to receive echoes. A receiver for processing the output of the transducer is gain and bandwidth controlled and produces a range signal whose duration is proportional to subject range. Proper operation requires the receiver to be blanked both during the transmission of the burst and for a predetermined time thereafter. The latter operation is necessary in order to permit ringing of the transducer to terminate since only after such termination can the output of the receiver be associated with an echo. The time period that the receiver must be blanked depends on such parameters as the duration and power of the burst, etc., and for a 1 millisecond burst about 600 microseconds following the burst is required for the ringing to subside significantly and permit the receiver to begin operation. Thus, for a 1 millisecond burst, the receiver is disabled for about 1.6 milliseconds, with the result that a subject no closer than about 10 inches from the transducer can be detected. While this minimum subject distance is adequate for most camera work, in some instances and in other applications of ultrasonic ranging, detections of subjects closer than 10 inches is desirable.
In order to decrease or vary the effective range of the sonic rangefinder, it is proposed as, for example, in U.S. Pat. No. 4,199,246, supra, that several different pulses could be used, one for each of several different ranges. For example, a short pulse could be used for objects from 10 centimeters to one meter and a second and longer pulse could be used for longer distances. How such a system could be implemented is fully explained in U.S. patent application Ser. No. 296,508.
Polaroid Corporation manufactures and sells both ultrasonic rangefinder cameras and ultrasonic rangefinder designer's kits for general use by engineers in designing a wide variety of systems which utilize sonic rangefinders. The general purpose sonic rangefinder designer kits are highly versatile so as to enable the engineer to integrate the designer's kit into a wide variety of different systems. Thus, the circuitry for the designer's kit must be designed so as to enable the kit user to control a broad variety of functions within the rangefinder that would otherwise be controlled automatically when the rangefinder is utilized in a camera apparatus.
Therefore, it is a primary object of this invention to provide a sonic rangefinder system that is compatible for use in either a sonic rangefinder camera or a general purpose sonic rangefinder designer's kit wherein many of the sonic rangefinding functions which are automatically provided within the camera apparatus may be independently controlled by the user when the sonic rangefinder is utilized in the designer's kit.
It is an even further object of this invention to provide a sonic rangefinder system which may be embodied in a single, digital integrated circuit chip which is compatible for use in either an automatic sonar rangefinder camera or a general purpose sonar rangefinder designer's kit.
Other objects of the invention will be in part obvious and will in part appear hereinafter. The invention accordingly comprises a mechanism and system possessing a construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosure.